Pressure limiting valves serve to limit a system pressure. They may have the form of directly controlled seat valves. Other designs are spool valves or disk valves. These, too, may fundamentally be vibrationally damped by the kind of damping presently applied, if they are controlled directly. Furthermore the piloted design is also possible. When a pre-set maximum pressure is exceeded, a connection from a pressure port to a return port is opened via the pressure limiting valve. In the most simple case the pressure limiting valves are controlled directly and thus have a simple construction and may be manufactured at low cost. Such directly controlled pressure limiting valves have high opening dynamics, so that pressure peaks in the system may be reduced very rapidly. It is one drawback of these pressure limiting valves, however, that they are very prone to vibration due to their opening dynamics in the event of pressure fluctuations. The valve bodies, which vibrate owing to hydraulic excitation, may result in a considerable acoustic load, and in unfavorable cases in the destruction of an associated valve seat or of the spring acting in the closing direction.
In order to attentuate these vibrations, pressure limiting valves are provided with damping means as described, e.g., in Bosch-Rexroth data sheet RC 25 402/08.97.
In this known solution, there is associated to the valve body on the pressure port side a damping piston which defines, jointly with a damping sleeve applied on the end side, a damping gap whereby a damping chamber is connected with a valve seat-side space. In the event of axial movements of the valve body, the volume of the damping chamber is modified so that pressure medium must flow out from it or into it. This pressure medium volume balance is impaired by the throttle effect in the damping gap, with kinetic energy of the valve body and of the damping piston being converted into heat, and the axial translation of the valve body thus being decelerated and damped.
It is a drawback in this known solution that the axial structural space of the pressure limiting valve is increased by the damping chamber connected on the pressure port side and having the damping piston arranged in it. Moreover a comparative technological complexity is necessary in the manufacture, for the pressure port has to be formed by oblique bores that are difficult to produce.
As an alternative solution it is also possible to provide not a pressure port-side damping device but a return-side damping device, wherein a damping chamber is filled with pressure medium and connected with the return port via the damping gap. In the event of axial translations of a damping piston that is connected with the valve body, pressure medium is displaced via the damping gap from the damping chamber or into the latter, so that the axial movements of the valve body are damped.
It is a drawback in this return-side low-pressure damping that 100% filling of the damping chamber with pressure medium must always be ensured. This filling may only be carried out with comparative complexity during installation of the valve. If air bubbles remain in the damping chamber, they deactivate this damping. Owing to the connection with the return port, an entry of air through the damping gap can not be excluded. This risk is particularly high if the return line is capable of being emptied entirely, or if air dissolved in the pressure medium bubbles out in the transition from high pressure to low pressure.